BACKGROUND:This mysterious sludge only appeared on Isle Delfino. It came from Shadow Mario(a.k.a. Bowser Junior), and covered the entire Island. Graffiti was generated by Shadow Mario using his Magic Paint Brush, invented by Prof. E. Gadd.
This slimy sludge was capable of completely covering things, such as trees, buildings, and even Piantas and Nokis! The Graffiti disappeared after the flood, and no one has seen it since.